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Wednesday, January 18, 2017

N8NM's SAVED VFO 30 Meter Rig


In early December Steve Murphy N8NM picked up this "mystery box" at a hamfest.   Dr. Juliano identified it as an old CB VFO.  Even though Steve is deeply committed to the dark side of frequency generation (digital synthesis) I was able to convince him to put this VFO to legitimate and proper amateur radio use AS AN ANALOG VFO.  I mean just look at that dial!  It would be a sin to connect that beautiful mechanism to a rotary encoder.   We see the results below.


Bill: 

The 30m rig that I had hoped to have QRV for SKN is finally ready to hit the airwaves!  I still have a few odds and ends to tidy up, but it's essentially done.

Where I ran into problems was my original choice of IF and VFO frequencies: I'd gone with a 13.51 MHz IF because I had the rocks, but that put the 3rd harmonic of the VFO right in the middle of the band.  Oops.
Moving the IF to 13.56 fixed that problem, but I still had a spur from that harmonic that needed to be filtered.  At first, it looked like a trap on the output of the VFO would squish it, but it ended up requiring a few extra poles of bandpass filtering to get it below -40 dB/c.  Now we're legal.
Anyway, here's a few pics. The chassis are bent from 22 ga aluminum on my trusty Harbor Freight brake.  They're almost square, they look cockeyed because I still need to make brackets to hold the top and bottom together.  The heat sink is overkill for 5 watts, but it was cheap :-)
Electronically, almost everything between the audio and power amps is straight-up Bitx.  The power amp uses a RD16HHF1 driven by my spin on Farhan's RF-386, and the audio is an LM380 driven by an LM324, with gating between CW and digital mode input handled by a CD4066.  The CW tone generator is based on WB0RIO's "clickless" sidetone circuit, which, while a little complicated, creates perfectly formed CW elements that really sound nice.
I'm still amazed at the stability of the LC VFO; I was monitoring JT65 signals over the weekend and noticed zero drift after warm-up.  To keep it ready to rock, it's powered from the "hot" side of the on/off switch, as is the CW oscillator. 
I can't think of much else to say about it...  It is what it is :-)
73 - Steve N8NM

Monday, January 16, 2017

Of Waterfalls, SDRs, and Homebrew Analog Rigs: Words of Wisdom from W8JI

W8JI

It happened again today. Conditions were good and I was BOOMING into the NYC area on 40 meters.  40 over.  Everyone liked the signal and said it sounded great.  Except for one anonymous grump who chimed in to say that I was "9 kc wide."  I imagine he was basing this on a quick look at his super-dooper SDR waterfall, without any consideration of signal strength or the characteristics of his own receiver. Sigh.  The Waterfall Police had struck again.  

OM W8JI gives a great description of the pitfalls of this kind of "you're-too-wide-because-my waterfall-says-so" reasoning.  Check it out.  And keep it handy in preparation for your next encounter with the 40 meter Waterfall Police.  

https://www.w8ji.com/checking_bandwidth_with_receiver.htm

Sunday, January 15, 2017

Wonderful "QSO Today" Interview with Ian Keyser G3ROO

N2CQR and G3ROO

I knew it was going to be a good Sunday morning in the shack when I saw that Eric 4Z1UG had posted an interview with Ian Keyser G3ROO.   This wonderful interview brought back memories of my visit to G3ROO's amazing facility in Dover.  (Thanks to Tony Fishpool who brought me out there.)

In this interview, you will hear Ian state -- in a very nonchalant English way -- that he built his first receiver at age 8.  And I really loved the story of how Ian got his call sign.  FB Ian.  

Ian is a very prominent member of the G-QRP club.  I was oddly relieved to learn that he is working on a LEGAL LIMIT LINEAR AMPLIFIER.  I hope he has special dispensation from Rev. George Dobbs.  I intend to cite this project if we ever have to defend Pete Juliano from charges of QROism.

Listen to the interview here:



That is a key designed for use aboard a hydrogen balloon.  This is the kind of thing that Ian has in his shack.
 
This is Ian's variometer -- mentioned in the interview.

That's me using one of  Ian's spy sets. 

Ian's antenna book:

Here are the SolderSmoke Daily News posts about Ian and the Dover Construction Club:



Saturday, January 14, 2017

BITX40 to BITX40 In Australia -- Both Rigs on the Beach, Video at Both Ends



There is so much great homebrewing going on down-under.   It makes me jealous.  And so much of it is for phone.  FB.

I really like VK3YE's sand graphic proclaiming to the world (or at least to the beach!) that a BITX40 to BITX40 contact had been made. 

Looks like both rigs were using VK3YE's ceramic resonator mod for the VFO.

Be sure to check out the BITX 40 Mods blog:
http://bitxhacks.blogspot.com

Thursday, January 12, 2017

N6ORS's Franken-SDR Superhet


Of course, I love it.  MOSFETS!  NE602's!  10.7 Mc IF cans!  Cycles, not hertz! And a Tayloe Quadrature Sampling Detector made from junkbox parts from the Reagan administration. FB Keith.   And the frequency display is icing on the cake.  

Bill:

I thought the group might find my new Franken-SDR interesting.
It is an SDR with a superhet front end. 


I wanted to play with an SDR but I didn't want to get a kit or buy
parts, so I scrounged through he drawers and found a mux chip
cd-4016 circa-1980 some old 7400 logic that is probably per-1980.
This could make a QSD but only very low frequencies. Well I thought
how about at IF frequencies?


The frontend is a MOSFET mixer (1975) , the 10.7 IF is a dual gate MOSFET
(1975), the second mixer is a NE602, the IF cans are all stagger tuned to
give a bandwidth of 50kcs.
The only thing modern is the DDS but I old-time-ifyed it with BCD switches.


Keith N6ORS





VK6FTH did something similar: http://www.vk6fh.com/vk6fh/SDRradio.htm


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